From his previous two shows, we knew that Jeff Mangum was playing an hour set, then coming back for a 20-minute encore. When he left the stage after that, I headed for the exit. But the standing ovation grew louder with each passing minute and the audience stayed in their seats, even after the nervous New England Conservatory ushers turned on the house lights and turned up the PA and opened wide the swinging doors to one of America's most acoustically perfect stages. The applause turned to a roar, and the seats rattled with stomp and with shout. Eventually, looking somewhat overwhelmed and not quite sure what to do, Mangum came back out for one more song.

Mangum looks taller and healthier and happier than I remember him from Neutral Milk Hotel's heyday. He wore a porkpie hat, a cowboy shirt, corduroy slacks, black sox, sensible shoes. He performed sitting down, in a simple chair, with four guitars and a music stand arrayed within easy reach. Earlier he'd joked that the last time he'd sang these songs it was in a basement for 30 people. Now he sang, as if in answer to a question that no one had asked but everyone was considering, "Well, now first of all/We became what we always had feared."

That's the first line of "Ferris Wheels on Fire," a song that didn't make either of Neutral Milk Hotel's two perfect albums. It was written around 1993. But hearing its final, waltz-time verse as a final word on the evening of September 10 was uncanny:

"But now, most of allI am holding you under my skinWatch these buildings fallWatch as each weak resistance caves inAll over you, all overAnd now finally fading from viewIs everything we ever knew"

So many of Mangum's songs, we were reminded, straddle the unthinkable and the sublime. They can be violent songs and he sings them violently, his reedy voice suddenly shouting. He is the most arresting lyricist of his generation -- stringing together beguiling imagery while pursuing obsessive story arcs that bend and bloom over the course of songs and albums -- as well as one of its strangest singers. Many of his best songs use nothing more advanced than a few major chords. In the late '90s, before indie-rock regenerated, Neutral Milk Hotel were an open secret -- critically acclaimed but without any evident commercial potential. You could tell people that he was the greatest songwriter of our time, but that didn't mean you expected anyone to listen. Still, when Mangum dropped out of active duty after Neutral Milk Hotel's stunning second album, In the Aeroplane Over the Sea, it seemed an inconceivable loss that there would be no follow-up. As the years passed, Mangum fell onto the list of people you assumed you'd never see again; it wasn't entirely clear that he was capable of performing.

Thus the sheer pandemonium that greeted his re-emergence this year. Part of the shock of seeing Mangum perform is how strange it is that he is here at all. It's like seeing a ghost.

The other part is that he sounds fucking great.

There used to be places in Neutral Milk Hotel's songs where you felt he was shouting to obscure a note; at Jordan Hall he kept surprising you with some new melody where none used to exist. Over the years there've been rumors that Mangum is batty or difficult to communicate with. (Having interviewed him once, just before Aeroplane came out, I can attest to the fact that he sometimes had trouble explaining himself, but I think anyone who'd written songs like that might have a tough time elaborating on them.) No evidence for that here: after an awkward start, he bantered easily with his adoring audience -- answering questions between songs (last show he attended, in case you were wondering: Tinariwen), inviting people to sing along, reaching to breach the sterility of the setting, to make a connection across the void.

It was a gig without a gimmick. He he sat in a chair with a guitar and sang his songs for an hour and a half, more or less as they were written. (He played one cover, Daniel Johnston's "True Love Will Find You In the End.") Everyone in the room, it is safe to say, knew these songs by heart. Somehow the performance was still a revelation. When Neutral Milk Hotel played a Providence warehouse in April of 1997 as part of the weekend-long Terrastock fest, Aeroplane was nearly a year from release, and Mangum walked onstage alone and played "Oh Comely," a rambling seven-minute ballad, most of it sung atop two chords. Over the years I've remembered that moment as being shocking because the song was new, the blunt force of being hit with it unexpectedly as being irreproducible, but at Jordan Hall he opened with it again -- and even if you know what's coming, those "pretty, bright and bubbly, terrible things" he sings about still have the power to bowl you over.

At some point it hit me that if Mangum is well enough to perform this beautifully, perhaps he's well enough to write another batch of these songs. If he's got new ones, he's keeping them to himself for now -- although "Ferris Wheels on Fire" is among a group of previously-unreleased NMH songs that will be part of a box set appearing in November.

Mangum played broad swaths of both Aeroplane and On Avery Island. The tone ranged from soft ecstasy of his surrealist children's song "Engine" to the punk-speed "Gardenhead" delivered with a quivering leg and hitting two yelping peaks that have always seemed to define the imperatives of Neutral Milk Hotel music: the verse that begins "Leave me alone!" and the one that begins "Follow me through!" At Jordan Hall it felt, at long last, like he might have had enough of the former, and be ready to lead the way again.